Drug used to reduce anxiety, fear, tension, agitation, and related disturbed mental states. Major tranquilizers (antipsychotic agents, or neuroleptics) are used to treat schizophrenia and other psychoses; phenothiazines, including chlorpromazine, are the best known. They are thought to block the activity of the neurotransmitterdopamine in the brain. Minor tranquilizers (antianxiety agents, or anxiolytics) are used to treat anxiety and tension; they are usually benzodiazepines, including diazepam (Valium) and chlordiazepoxide (Librium). They have a calming effect and reduce both physical and psychological effects of anxiety, fear, and stress by enhancing the action of the neurotransmitter gamma-aminobutyric acid (GABA) in the brain.